(You all just knew I was gonna drop in. Admit it.

)
Needless to say...I completely disagree with the OP. Ezri is one of my favorite characters in the
Trek universe. She
was needed, thematically, as the show hadn't had her kind of personality on a regular basis in a LONG time. Story-wise, her presence was a
constant symbolic reminder in the final season that "life marches on"--an element of hope, that the darkness is temporary--that "we will recover".
And as a straight guy with a thing for said kind of personality, I'm glad she wasn't a guy.

Besides...while I'm all for "dramatic potential", the simple fact was
the series was almost over. No need to make things more complicated than they had to be. Better to give emotional
closure to the characters--Sisko, Worf, and Bashir in particular, but also Quark. Sisko had to overcome the depression he got after losing Jadzia...and the other three had to deal with their respective relationships/feelings involving Dax. Somehow, I doubt the Ninth Dax being a man would've helped much, on that.